In this study, the oxide layer on 6061 Al alloy was produced in a free-alkali ion electrolyte containing calcium phosphate and ammonia water by PEO method. Microstructure, micro-hardness and corrosion resistance of PEO coated were investigated and discussed. Surface morphology analysis indicated the coating characterized by micro-pores, pan-cakes like, and micro-crakes with pore size and percentage of pores on coating surface are smaller than 1 μm and %, respectively. | Journal of Science and Technology 54 (5A) (2016) 151-158 PLASMA ELECTROLYTIC OXIDATION COATING ON 6061 AL ALLOY USING AN ELECTROLYTE WITHOUT ALKALI IONS Quang-Phu Tran1, 2, *, Tsung-Shune Chin2 1 Department of Electrical and Electronic Engineering, Hung Yen University of Technology and Education, 39A Road, Dan Tien Commune, Khoai Chau District, Hung Yen Province, Vietnam 2 Department of Materials Science and Engineering, Feng Chia University, No. 100, Wenhua Road, Xitun District, Taichung City, Taiwan 407 * Email: tranquangphu@ Received: 15 July 2016; Accepted for publication: 4 December /2016 ABSTRACT Plasma electrolytic oxidation (PEO) technique is well known to use for modifying the surface of valve metal such as Al, Mg and Ti, which improves mechanical and corrosion resistance properties. PEO is an electrochemical process of oxidation by creating microdischarges on the surface of metal immersed in an electrolyte under applying a high voltage. Electrolyte used in PEO process is almost based on alkali ions such as Na ion. The report on PEO process using free-alkali ion is very rare. In this study, the oxide layer on 6061 Al alloy was produced in a free-alkali ion electrolyte containing calcium phosphate and ammonia water by PEO method. Microstructure, micro-hardness and corrosion resistance of PEO coated were investigated and discussed. Surface morphology analysis indicated the coating characterized by micro-pores, pan-cakes like, and micro-crakes with pore size and percentage of pores on coating surface are smaller than 1 μm and %, respectively. Micro-hardness and corrosion resistance of PEO coated are greatly improved compared to the bare Al alloy. Free-alkali-ions in oxide layer coated on Al alloy is important for many applications today. Keywords: plasma electrolytic oxidation; free-alkali ion; 6061 Al alloy; micro-hardness; corrosion resistance. 1. INTRODUCTION Al alloys are increasingly used in a variety of industries due to many their
